Mark Twain once famously said, "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so," and boy is that true. Many people waltz around their lives spouting off complete bullshit, and these are 9 examples that really grind my gears the most.

1. We only use 10% of our brains.

If you only used 10% of your brain, you'd probably be dead. At any given moment, we may only use 10% of our brains for a certain task, but rest assured, the brain is not like a partially filled thumb drive. You use all of it.

2. Shaving makes your hair grow back faster, thicker.

False. Shaving does not make your hair grow back thicker. Some people think it does because over time, your hair becomes thinner at the ends, so when you shave, it seems to be thicker at the base.

3. Tar in cigarettes causes cancer.

Tar and nicotine aren't actually the issue. The issue is the smoke itself. Smoke in the lungs causes cancer. Polonium and radon found in the smoke causes most of the cancer relating to smoking.

4. Cold doesn't make you sick.

This is actually wrong, being cold can make you sick by suppressing your immune system. When suppressed, the immune system can't block infectious disease so well.

5. Your hair and finger nails continue to grow after death.

The only thing growing on you after death are the delightful little bacteria breaking down your body. Hair and finger nails don't grow. They just appear to grow longer because, as we begin to decay, our skin tightens, making them seem longer.

6. The big bang was an explosion.

The "big bang" was actually coined by someone who didn't believe in the concept, asking "What, was there some kind of big bang?" There actually wasn't an explosion at all. The Big Bang was simply an expansion of space.